merges r30648 from trunk into ruby_1_9_2.

--
* string.c (rb_string_value_cstr): rb_str_modify can change
  RSTRING_PTR.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_1_9_2@30694 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

1 files changed, 5 insertions, 1 deletions

diff --git a/string.c b/string.c
index 542aaff0ee..368eb63463 100644
--- a/string.c
+++ b/string.c
@@ -1381,7 +1381,11 @@ rb_string_value_cstr(volatile VALUE *ptr)
     if (!s || memchr(s, 0, len)) {
 	rb_raise(rb_eArgError, "string contains null byte");
     }
-    if (s[len]) rb_str_modify(str);
+    if (s[len]) {
+	rb_str_modify(str);
+	s = RSTRING_PTR(str);
+	s[RSTRING_LEN(str)] = 0;
+    }
     return s;
 }